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ACI 318M-11

Building Code Requirements for
Structural Concrete (ACI 318M-11)
An ACI Standard

and Commentary

Reported by ACI Committee 318


First Printing
September 2011
American Concrete Institute

®

Advancing concrete knowledge

Building Code Requirements for Structural Concrete (ACI 318M-11)
and Commentary
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BUILDING CODE REQUIREMENTS FOR
STRUCTURAL CONCRETE (ACI 318M-11)
AND COMMENTARY
REPORTED BY ACI COMMITTEE 318
ACI Committee 318
Structural Building Code
Voting Main Committee Members
Randall W. Poston
Chair
Sergio M. Alcocer
Neal S. Anderson
Florian G. Barth
Roger J. Becker
Kenneth B. Bondy
Dean A. Browning
James R. Cagley
Ned M. Cleland
W. Gene Corley
Charles W. Dolan

Basile G. Rabbat
Secretary

Anthony E. Fiorato
Catherine E. French
Robert J. Frosch
Luis E. García
Satyendra Ghosh
Harry A. Gleich

David P. Gustafson
James R. Harris
Terence C. Holland
Shyh-Jiann Hwang

James O. Jirsa
Dominic J. Kelly
Gary J. Klein
Ronald Klemencic
Cary S. Kopczynski
Colin L. Lobo
Paul F. Mlakar
Jack P. Moehle
Gustavo J. Parra-Montesinos
Julio A. Ramirez

David M. Rogowsky
David H. Sanders
Guillermo Santana
Thomas C. Schaeffer
Stephen J. Seguirant
Andrew W. Taylor
Eric M. Tolles
James K. Wight
Sharon L. Wood
Loring A. Wyllie Jr.

Voting Subcommittee Members
F. Michael Bartlett
Raul D. Bertero

Allan P. Bommer
JoAnn P. Browning
Nicholas J. Carino
Ronald A. Cook
David Darwin
Lisa R. Feldman

Kevin J. Folliard
H. R. Trey Hamilton III
R. Doug Hooton
Kenneth C. Hover
Steven H. Kosmatka
Michael E. Kreger
Jason J. Krohn
Daniel A. Kuchma

Andres Lepage
Raymond Lui
LeRoy A. Lutz
Joseph Maffei
Donald F. Meinheit
Fred Meyer
Denis Mitchell

Theodore A. Mize
Suzanne Dow Nakaki
Theodore L. Neff
Lawrence C. Novak
Viral B. Patel
Conrad Paulson

Jose A. Pincheira

Mario E. Rodriguez
Bruce W. Russell
M. Saiid Saiidi
Andrea J. Schokker
John F. Stanton
Roberto Stark
John W. Wallace

International Liaison Members
Mathias Brewer
Josef Farbiarz
Luis B. Fargier-Gabaldon

Alberto Giovambattista
Hector D. Hernandez
Angel E. Herrera

Hector Monzon-Despang
Enrique Pasquel
Patricio A. Placencia

Oscar M. Ramirez
Fernando Reboucas Stucchi
Fernando Yáñez

Consulting Members
John E. Breen
Neil M. Hawkins

H. S. Lew
James G. MacGregor

Robert F. Mast
Charles G. Salmon



BUILDING CODE REQUIREMENTS FOR
STRUCTURAL CONCRETE (ACI 318M-11)
AND COMMENTARY
REPORTED BY ACI COMMITTEE 318

PREFACE
The “Building Code Requirements for Structural Concrete” (“Code”) covers the materials, design, and construction
of structural concrete used in buildings and where applicable in nonbuilding structures. The Code also covers the
strength evaluation of existing concrete structures.
Among the subjects covered are: contract documents; inspection; materials; durability requirements; concrete
quality, mixing, and placing; formwork; embedded pipes; construction joints; reinforcement details; analysis and
design; strength and serviceability; flexural and axial loads; shear and torsion; development and splices of reinforcement;
slab systems; walls; footings; precast concrete; composite flexural members; prestressed concrete; shells and folded
plate members; strength evaluation of existing structures; provisions for seismic design; structural plain concrete; strutand-tie modeling in Appendix A; alternative design provisions in Appendix B; alternative load and strength reduction
factors in Appendix C; and anchoring to concrete in Appendix D.
The quality and testing of materials used in construction are covered by reference to the appropriate ASTM standard
specifications. Welding of reinforcement is covered by reference to the appropriate American Welding Society (AWS)
standard.
Uses of the Code include adoption by reference in general building codes, and earlier editions have been widely used
in this manner. The Code is written in a format that allows such reference without change to its language. Therefore,
background details or suggestions for carrying out the requirements or intent of the Code portion cannot be included.

The Commentary is provided for this purpose. Some of the considerations of the committee in developing the Code
portion are discussed within the Commentary, with emphasis given to the explanation of new or revised provisions.
Much of the research data referenced in preparing the Code is cited for the user desiring to study individual questions
in greater detail. Other documents that provide suggestions for carrying out the requirements of the Code are also cited.
Keywords: admixtures; aggregates; anchorage (structural); beam-column frame; beams (supports); building codes; cements; cold weather construction;
columns (supports); combined stress; composite construction (concrete and steel); composite construction (concrete to concrete); compressive strength;
concrete construction; concrete slabs; concretes; construction joints; continuity (structural); contract documents; contraction joints; cover; curing; deep
beams; deflections; earthquake-resistant structures; embedded service ducts; flexural strength; floors; folded plates; footings; formwork (construction); frames;
hot weather construction; inspection; isolation joints; joints (junctions); joists; lightweight concretes; load tests (structural); loads (forces); materials; mixing; mixture
proportioning; modulus of elasticity; moments; pipe columns; pipes (tubing); placing; plain concrete; precast concrete; prestressed concrete; prestressing steels;
quality control; reinforced concrete; reinforcing steels; roofs; serviceability; shear strength; shear walls; shells (structural forms); spans; splicing; strength; strength
analysis; stresses; structural analysis; structural concrete; structural design; structural integrity; T-beams; torsion; walls; water; welded wire reinforcement.

ACI 318M-11 was adopted as a standard of the American Concrete
Institute May 24, 2011, to supersede ACI 318M-08 in accordance with the
Institute’s standardization procedure and was published October 2011.
A complete U.S Customary unit companion to ACI 318M has been
developed, 318; U.S Customary equivalents are provided only in Appendix F
of this document.
ACI Committee Reports, Manuals, Guides, Standard Practices, and
Commentaries are intended for guidance in planning, designing, executing,
and inspecting construction. This Commentary is intended for the use of
individuals who are competent to evaluate the significance and limitations
of its content and recommendations, and who will accept responsibility for
the application of the material it contains. The American Concrete Institute

disclaims any and all responsibility for the stated principles. The Institute
shall not be liable for any loss or damage arising therefrom. Reference to
this Commentary shall not be made in contract documents. If items found
in this Commentary are desired by the licensed design professional to be

a part of the contract documents, they shall be restated and incorporated
in mandatory language.
Copyright © 2011, American Concrete Institute.
All rights reserved including rights of reproduction and use in any form
or by any means, including the making of copies by any photo process, or
by any electronic or mechanical device, printed or written or oral, or
recording for sound or visual reproduction or for use in any knowledge or
retrieval system or device, unless permission in writing is obtained from the
copyright proprietors.

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STRUCTURAL CONCRETE BUILDING CODE (ACI 318M-11) AND COMMENTARY

CONTENTS
INTRODUCTION ...................................................................................................................................... 7
CHAPTER 1—GENERAL REQUIREMENTS .......................................................................................... 9
1.1—Scope ..............................................................................................................................................................................9
1.2—Contract documents ......................................................................................................................................................14
1.3—Inspection ......................................................................................................................................................................15
1.4—Approval of special systems of design or construction..................................................................................................17

CHAPTER 2—NOTATION AND DEFINITIONS..................................................................................... 19
2.1—Code notation ................................................................................................................................................................19
2.2—Definitions......................................................................................................................................................................29

CHAPTER 3—MATERIALS ................................................................................................................... 43

3.1—Tests of materials ..........................................................................................................................................................43
3.2—Cementitious materials ..................................................................................................................................................43
3.3—Aggregates ....................................................................................................................................................................44
3.4—Water .............................................................................................................................................................................44
3.5—Steel reinforcement .......................................................................................................................................................45
3.6—Admixtures.....................................................................................................................................................................50
3.7—Storage of materials ......................................................................................................................................................51
3.8—Referenced standards ...................................................................................................................................................51

CHAPTER 4—DURABILITY REQUIREMENTS .................................................................................... 57
4.1—General..........................................................................................................................................................................57
4.2—Exposure categories and classes..................................................................................................................................57
4.3—Requirements for concrete mixtures..............................................................................................................................59
4.4—Additional requirements for freezing-and-thawing exposure .........................................................................................62
4.5—Alternative cementitious materials for sulfate exposure ................................................................................................63

CHAPTER 5—CONCRETE QUALITY, MIXING, AND PLACING ......................................................... 65
5.1—General..........................................................................................................................................................................65
5.2—Selection of concrete proportions ..................................................................................................................................66
5.3—Proportioning on the basis of field experience or trial mixtures, or both ........................................................................66
5.4—Proportioning without field experience or trial mixtures .................................................................................................71
5.5—Average compressive strength reduction ......................................................................................................................71
5.6—Evaluation and acceptance of concrete.........................................................................................................................72
5.7—Preparation of equipment and place of deposit .............................................................................................................77
5.8—Mixing ............................................................................................................................................................................78
5.9—Conveying......................................................................................................................................................................78
5.10—Depositing....................................................................................................................................................................79
5.11—Curing ..........................................................................................................................................................................79
5.12—Cold weather requirements .........................................................................................................................................80
5.13—Hot weather requirements ...........................................................................................................................................81

CHAPTER 6—FORMWORK, EMBEDMENTS, AND CONSTRUCTION JOINTS................................. 83
6.1—Design of formwork........................................................................................................................................................83
6.2—Removal of forms, shores, and reshoring......................................................................................................................83
6.3—Embedments in concrete...............................................................................................................................................85
6.4—Construction joints .........................................................................................................................................................86

CHAPTER 7—DETAILS OF REINFORCEMENT .................................................................................. 89
7.1—Standard hooks .............................................................................................................................................................89
7.2—Minimum bend diameters ..............................................................................................................................................89
7.3—Bending .........................................................................................................................................................................90
7.4—Surface conditions of reinforcement ..............................................................................................................................90
7.5—Placing reinforcement....................................................................................................................................................91
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7.6—Spacing limits for reinforcement ................................................................................................................................... 92
7.7—Concrete protection for reinforcement .......................................................................................................................... 93
7.8—Reinforcement details for columns ............................................................................................................................... 96
7.9—Connections.................................................................................................................................................................. 97
7.10—Transverse reinforcement for compression members ................................................................................................ 98
7.11—Transverse reinforcement for flexural members ....................................................................................................... 101
7.12—Shrinkage and temperature reinforcement ............................................................................................................... 101
7.13—Requirements for structural integrity......................................................................................................................... 104

CHAPTER 8—ANALYSIS AND DESIGN—GENERAL CONSIDERATIONS .......................... 107

8.1—Design methods.......................................................................................................................................................... 107
8.2—Loading ....................................................................................................................................................................... 107
8.3—Methods of analysis .................................................................................................................................................... 108
8.4—Redistribution of moments in continuous flexural members ....................................................................................... 109
8.5—Modulus of elasticity ................................................................................................................................................... 111
8.6—Lightweight concrete................................................................................................................................................... 111
8.7—Stiffness ...................................................................................................................................................................... 112
8.8—Effective stiffness to determine lateral deflections ...................................................................................................... 112
8.9—Span length................................................................................................................................................................. 113
8.10—Columns.................................................................................................................................................................... 114
8.11—Arrangement of live load........................................................................................................................................... 114
8.12—T-beam construction ................................................................................................................................................. 115
8.13—Joist construction ...................................................................................................................................................... 116
8.14—Separate floor finish.................................................................................................................................................. 117

CHAPTER 9—STRENGTH AND SERVICEABILITY REQUIREMENTS............................................. 119
9.1—General ....................................................................................................................................................................... 119
9.2—Required strength ....................................................................................................................................................... 119
9.3—Design strength........................................................................................................................................................... 122
9.4—Design strength for reinforcement .............................................................................................................................. 126
9.5—Control of deflections .................................................................................................................................................. 126

CHAPTER 10—FLEXURE AND AXIAL LOADS ................................................................................. 135
10.1—Scope........................................................................................................................................................................ 135
10.2—Design assumptions ................................................................................................................................................. 135
10.3—General principles and requirements........................................................................................................................ 137
10.4—Distance between lateral supports of flexural members ........................................................................................... 140
10.5—Minimum reinforcement of flexural members............................................................................................................ 140
10.6—Distribution of flexural reinforcement in beams and one-way slabs.......................................................................... 141
10.7—Deep beams ............................................................................................................................................................. 143

10.8—Design dimensions for compression members ......................................................................................................... 144
10.9—Limits for reinforcement of compression members................................................................................................... 144
10.10—Slenderness effects in compression members ....................................................................................................... 146
10.11—Axially loaded members supporting slab system .................................................................................................... 154
10.12—Transmission of column loads through floor system............................................................................................... 154
10.13—Composite compression members ......................................................................................................................... 155
10.14—Bearing strength ..................................................................................................................................................... 158

CHAPTER 11—SHEAR AND TORSION ............................................................................................. 161
11.1—Shear strength .......................................................................................................................................................... 161
11.2—Shear strength provided by concrete for nonprestressed members......................................................................... 164
11.3—Shear strength provided by concrete for prestressed members............................................................................... 166
11.4—Shear strength provided by shear reinforcement...................................................................................................... 169
11.5—Design for torsion...................................................................................................................................................... 174
11.6—Shear-friction ............................................................................................................................................................ 186
11.7—Deep beams ............................................................................................................................................................. 189
11.8—Provisions for brackets and corbels.......................................................................................................................... 190
11.9—Provisions for walls ................................................................................................................................................... 194
11.10—Transfer of moments to columns ............................................................................................................................ 196
11.11—Provisions for slabs and footings ............................................................................................................................ 196
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STRUCTURAL CONCRETE BUILDING CODE (ACI 318M-11) AND COMMENTARY

CHAPTER 12—DEVELOPMENT AND SPLICES OF REINFORCEMENT ......................................... 209
12.1—Development of reinforcement—General ..................................................................................................................209
12.2—Development of deformed bars and deformed wire in tension ..................................................................................210

12.3—Development of deformed bars and deformed wire in compression .........................................................................212
12.4—Development of bundled bars....................................................................................................................................213
12.5—Development of standard hooks in tension ...............................................................................................................213
12.6—Development of headed and mechanically anchored deformed bars in tension .......................................................216
12.7—Development of welded deformed wire reinforcement in tension..............................................................................218
12.8—Development of welded plain wire reinforcement in tension .....................................................................................220
12.9—Development of prestressing strand..........................................................................................................................220
12.10—Development of flexural reinforcement—General ...................................................................................................222
12.11—Development of positive moment reinforcement .....................................................................................................225
12.12—Development of negative moment reinforcement....................................................................................................226
12.13—Development of web reinforcement.........................................................................................................................227
12.14—Splices of reinforcement—General..........................................................................................................................230
12.15—Splices of deformed bars and deformed wire in tension..........................................................................................231
12.16—Splices of deformed bars in compression................................................................................................................233
12.17—Splice requirements for columns .............................................................................................................................234
12.18—Splices of welded deformed wire reinforcement in tension .....................................................................................236
12.19—Splices of welded plain wire reinforcement in tension .............................................................................................237

CHAPTER 13—TWO-WAY SLAB SYSTEMS ..................................................................................... 239
13.1—Scope ........................................................................................................................................................................239
13.2—General......................................................................................................................................................................240
13.3—Slab reinforcement ....................................................................................................................................................241
13.4—Openings in slab systems..........................................................................................................................................244
13.5—Design procedures ....................................................................................................................................................244
13.6—Direct design method.................................................................................................................................................247
13.7—Equivalent frame method...........................................................................................................................................254

CHAPTER 14—WALLS ....................................................................................................................... 259
14.1—Scope ........................................................................................................................................................................259
14.2—General......................................................................................................................................................................259

14.3—Minimum reinforcement .............................................................................................................................................260
14.4—Walls designed as compression members ................................................................................................................261
14.5—Empirical design method ...........................................................................................................................................261
14.6—Nonbearing walls .......................................................................................................................................................262
14.7—Walls as grade beams ...............................................................................................................................................262
14.8—Alternative design of slender walls ............................................................................................................................263

CHAPTER 15—FOOTINGS ................................................................................................................. 267
15.1—Scope ........................................................................................................................................................................267
15.2—Loads and reactions ..................................................................................................................................................267
15.3—Footings supporting circular or regular polygon-shaped columns or pedestals ........................................................268
15.4—Moment in footings ....................................................................................................................................................268
15.5—Shear in footings........................................................................................................................................................269
15.6—Development of reinforcement in footings .................................................................................................................270
15.7—Minimum footing depth ..............................................................................................................................................270
15.8—Transfer of force at base of column, wall, or reinforced pedestal..............................................................................270
15.9—Sloped or stepped footings........................................................................................................................................272
15.10—Combined footings and mats...................................................................................................................................273

CHAPTER 16—PRECAST CONCRETE.............................................................................................. 275
16.1—Scope ........................................................................................................................................................................275
16.2—General......................................................................................................................................................................275
16.3—Distribution of forces among members......................................................................................................................276
16.4—Member design..........................................................................................................................................................276
16.5—Structural integrity......................................................................................................................................................277
16.6—Connection and bearing design.................................................................................................................................279
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STRUCTURAL CONCRETE BUILDING CODE (ACI 318M-11) AND COMMENTARY

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16.7—Items embedded after concrete placement .............................................................................................................. 281
16.8—Marking and identification ......................................................................................................................................... 281
16.9—Handling.................................................................................................................................................................... 281
16.10—Strength evaluation of precast construction............................................................................................................ 281

CHAPTER 17—COMPOSITE CONCRETE FLEXURAL MEMBERS.................................................. 283
17.1—Scope........................................................................................................................................................................ 283
17.2—General ..................................................................................................................................................................... 283
17.3—Shoring ..................................................................................................................................................................... 284
17.4—Vertical shear strength.............................................................................................................................................. 284
17.5—Horizontal shear strength.......................................................................................................................................... 284
17.6—Ties for horizontal shear ........................................................................................................................................... 285

CHAPTER 18—PRESTRESSED CONCRETE .................................................................................... 287
18.1—Scope........................................................................................................................................................................ 287
18.2—General ..................................................................................................................................................................... 288
18.3—Design assumptions ................................................................................................................................................. 289
18.4—Serviceability requirements—Flexural members ...................................................................................................... 290
18.5—Permissible stresses in prestressing steel................................................................................................................ 293
18.6—Loss of prestress ...................................................................................................................................................... 293
18.7—Flexural strength ....................................................................................................................................................... 294
18.8—Limits for reinforcement of flexural members............................................................................................................ 296
18.9—Minimum bonded reinforcement ............................................................................................................................... 296
18.10—Statically indeterminate structures.......................................................................................................................... 298
18.11—Compression members—Combined flexure and axial loads .................................................................................. 299
18.12—Slab systems .......................................................................................................................................................... 300
18.13—Post-tensioned tendon anchorage zones ............................................................................................................... 302

18.14—Design of anchorage zones for monostrand or single 16 mm diameter bar tendons ............................................. 307
18.15—Design of anchorage zones for multistrand tendons .............................................................................................. 309
18.16—Corrosion protection for unbonded tendons ........................................................................................................... 309
18.17—Post-tensioning ducts ............................................................................................................................................. 310
18.18—Grout for bonded tendons....................................................................................................................................... 310
18.19—Protection for prestressing steel ............................................................................................................................. 311
18.20—Application and measurement of prestressing force............................................................................................... 311
18.21—Post-tensioning anchorages and couplers.............................................................................................................. 312
18.22—External post-tensioning ......................................................................................................................................... 313

CHAPTER 19—SHELLS AND FOLDED PLATE MEMBERS ............................................................. 315
19.1—Scope and definitions ............................................................................................................................................... 315
19.2—Analysis and design.................................................................................................................................................. 317
19.3—Design strength of materials ..................................................................................................................................... 319
19.4—Shell reinforcement................................................................................................................................................... 319
19.5—Construction.............................................................................................................................................................. 321

CHAPTER 20—STRENGTH EVALUATION OF EXISTING STRUCTURES ...................................... 323
20.1—Strength evaluation—General .................................................................................................................................. 323
20.2—Determination of required dimensions and material properties ................................................................................ 324
20.3—Load test procedure.................................................................................................................................................. 325
20.4—Loading criteria ......................................................................................................................................................... 326
20.5—Acceptance criteria ................................................................................................................................................... 326
20.6—Provision for lower load rating .................................................................................................................................. 328
20.7—Safety........................................................................................................................................................................ 328

CHAPTER 21—EARTHQUAKE-RESISTANT STRUCTURES ........................................................... 329
21.1—General requirements ............................................................................................................................................... 329
21.2—Ordinary moment frames .......................................................................................................................................... 335
21.3—Intermediate moment frames.................................................................................................................................... 335

21.4—Intermediate precast structural walls ........................................................................................................................ 339
21.5—Flexural members of special moment frames........................................................................................................... 340
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STRUCTURAL CONCRETE BUILDING CODE (ACI 318M-11) AND COMMENTARY

21.6—Special moment frame members subjected to bending and axial load .....................................................................346
21.7—Joints of special moment frames ...............................................................................................................................350
21.8—Special moment frames constructed using precast concrete ....................................................................................354
21.9—Special structural walls and coupling beams.............................................................................................................356
21.10—Special structural walls constructed using precast concrete ...................................................................................365
21.11—Structural diaphragms and trusses..........................................................................................................................366
21.12—Foundations.............................................................................................................................................................371
21.13—Members not designated as part of the seismic-force-resisting system ..................................................................374

CHAPTER 22—STRUCTURAL PLAIN CONCRETE .......................................................................... 377
22.1—Scope ........................................................................................................................................................................377
22.2—Limitations .................................................................................................................................................................378
22.3—Joints .........................................................................................................................................................................378
22.4—Design method ..........................................................................................................................................................379
22.5—Strength design .........................................................................................................................................................380
22.6—Walls..........................................................................................................................................................................381
22.7—Footings.....................................................................................................................................................................382
22.8—Pedestals...................................................................................................................................................................384
22.9—Precast members ......................................................................................................................................................384
22.10—Plain concrete in earthquake-resisting structures....................................................................................................384

APPENDIX A—STRUT-AND-TIE MODELS ........................................................................................ 387
A.1—Definitions ...................................................................................................................................................................387
A.2—Strut-and-tie model design procedure.........................................................................................................................394
A.3—Strength of struts.........................................................................................................................................................396
A.4—Strength of ties ............................................................................................................................................................399
A.5—Strength of nodal zones ..............................................................................................................................................400

APPENDIX B—ALTERNATIVE PROVISIONS FOR REINFORCED AND PRESTRESSED
CONCRETE FLEXURAL AND COMPRESSION MEMBERS ................................................ 403
B.1—Scope ..........................................................................................................................................................................403

APPENDIX C—ALTERNATIVE LOAD AND STRENGTH REDUCTION FACTORS.......................... 411
C.9.1—Scope.......................................................................................................................................................................411
C.9.2—Required strength ....................................................................................................................................................411
C.9.3—Design strength........................................................................................................................................................413

APPENDIX D—ANCHORING TO CONCRETE ................................................................................... 417
D.1—Definitions ...................................................................................................................................................................417
D.2—Scope..........................................................................................................................................................................421
D.3—General requirements .................................................................................................................................................422
D.4—General requirements for strength of anchors ............................................................................................................430
D.5—Design requirements for tensile loading......................................................................................................................436
D.6—Design requirements for shear loading .......................................................................................................................450
D.7—Interaction of tensile and shear forces ........................................................................................................................461
D.8—Required edge distances, spacings, and thicknesses to preclude splitting failure .....................................................462
D.9—Installation and inspection of anchors.........................................................................................................................463

APPENDIX E—STEEL REINFORCEMENT INFORMATION .............................................................. 467
APPENDIX F—EQUIVALENCE BETWEEN SI-METRIC, MKS-METRIC, AND U.S. CUSTOMARY
UNITS OF NONHOMOGENOUS EQUATIONS IN THE CODE ............................................. 469

COMMENTARY REFERENCES .......................................................................................................... 477
INDEX ................................................................................................................................................... 497
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The ACI Building Code Requirements for Structural Concrete (“Code”) and Commentary are presented in a side-by-side
column format, with Code text placed in the left column and the corresponding Commentary text aligned in the right column.
To further distinguish the Code from the Commentary, the Code has been printed in Helvetica, the same type face in which
this paragraph is set.
This paragraph is set in Times Roman, and all portions of the text exclusive to the Commentary are printed in this type face. Commentary
section numbers are preceded by an “R” to further distinguish them from Code section numbers.
Substantive changes from 318M-08 are indicated with vertical lines in the margin (editorial changes not indicated).

INTRODUCTION
This Commentary discusses some of the considerations of
Committee 318 in developing the provisions contained in
“Building Code Requirements for Structural Concrete (ACI
318M-11),” hereinafter called the Code or the 2011 Code.
Emphasis is given to the explanation of new or revised
provisions that may be unfamiliar to Code users. In addition,
comments are included for some items contained in previous
editions of the Code to make the present commentary
independent of the previous editions. Comments on specific
provisions are made under the corresponding chapter and
section numbers of the Code.
The Commentary is not intended to provide a complete

historical background concerning the development of the
Code, nor is it intended to provide a detailed résumé of the
studies and research data reviewed by the committee in
formulating the provisions of the Code. However, references
to some of the research data are provided for those who wish
to study the background material in depth.
As the name implies, “Building Code Requirements for
Structural Concrete” is meant to be used as part of a legally
adopted building code and as such must differ in form and
substance from documents that provide detailed specifications,
recommended practice, complete design procedures, or
design aids.
The Code is intended to cover all buildings of the usual
types, both large and small. Requirements more stringent
than the Code provisions may be desirable for unusual
construction. The Code and Commentary cannot replace
sound engineering knowledge, experience, and judgment.
A building code states only the minimum requirements
necessary to provide for public health and safety. The Code
is based on this principle. For any structure, the owner or the
licensed design professional may require the quality of
materials and construction to be higher than the minimum
requirements necessary to protect the public as stated in the
Code. However, lower standards are not permitted.
*
For a history of the ACI Building Code, see Kerekes, F., and Reid, H. B., Jr., “Fifty
Years of Development in Building Code Requirements for Reinforced Concrete,” ACI
JOURNAL, Proceedings V. 50, No. 6, Feb. 1954, p. 441. For a discussion of code
philosophy, see Siess, C. P., “Research, Building Codes, and Engineering Practice,”
ACI JOURNAL, Proceedings V. 56, No. 5, May 1960, p. 1105.

The Commentary directs attention to other documents that
provide suggestions for carrying out the requirements and
intent of the Code. However, those documents and the
Commentary are not a part of the Code.
The Code has no legal status unless it is adopted by the
government bodies having the police power to regulate
building design and construction. Where the Code has not
been adopted, it may serve as a reference to good practice
even though it has no legal status.
The Code provides a means of establishing minimum standards
for acceptance of designs and construction by legally
appointed building officials or their designated representatives.
The Code and Commentary are not intended for use in settling
disputes between the owner, engineer, architect, contractor, or
their agents, subcontractors, material suppliers, or testing
agencies. Therefore, the Code cannot define the contract
responsibility of each of the parties in usual construction.
General references requiring compliance with the Code in the
project specifications should be avoided since the contractor is
rarely in a position to accept responsibility for design details or
construction requirements that depend on a detailed knowledge
of the design. Design-build construction contractors, however,
typically combine the design and construction responsibility.
Generally, the contract documents should contain all of the
necessary requirements to ensure compliance with the Code.
In part, this can be accomplished by reference to specific
Code sections in the project specifications. Other ACI
publications, such as “Specifications for Structural Concrete
(ACI 301M)” are written specifically for use as contract

documents for construction.
It is recommended to have testing and certification programs
for the individual parties involved with the execution of
work performed in accordance with this Code. Available for
this purpose are the plant certification programs of the
Precast/Prestressed Concrete Institute, the Post-Tensioning
Institute, and the National Ready Mixed Concrete Association; the personnel certification programs of the American
Concrete Institute and the Post-Tensioning Institute; and the
Concrete Reinforcing Steel Institute’s Voluntary Certification
Program for Fusion-Bonded Epoxy Coating Applicator
Plants. In addition, “Standard Specification for Agencies
Engaged in Construction Inspecting and/or Testing” (ASTM

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E329-09) specifies performance requirements for inspection
and testing agencies.
Design reference materials illustrating applications of the
Code requirements may be found in the following documents.
The design aids listed may be obtained from the sponsoring
organization.
Design aids:
“ACI Design Handbook,” Publication SP-17M(09), American Concrete Institute, Farmington Hills, MI, 2009, 252 pp.
(This provides tables and charts for design of eccentrically
loaded columns by the Strength Design Method of the 2005

Code. Provides design aids for use in the engineering design
and analysis of reinforced concrete slab systems carrying
loads by two-way action. Design aids are also provided for
the selection of slab thickness and for reinforcement required
to control deformation and assure adequate shear and
flexural strengths.)
“ACI Detailing Manual—2004,” ACI Committee 315,
Publication SP-66(04), American Concrete Institute, Farmington Hills, MI, 2004, 212 pp. (Includes the standard, ACI
315-99, and report, ACI 315R-04. Provides recommended
methods and standards for preparing engineering drawings,
typical details, and drawings placing reinforcing steel in
reinforced concrete structures. Separate sections define
responsibilities of both engineer and reinforcing bar detailer.)
“Guide to Durable Concrete (ACI 201.2R-08),” ACI
Committee 201, American Concrete Institute, Farmington
Hills, MI, 2008, 49 pp. (This describes specific types of
concrete deterioration. It contains a discussion of the
mechanisms involved in deterioration and the recommended
requirements for individual components of the concrete,
quality considerations for concrete mixtures, construction
procedures, and influences of the exposure environment.)
“Guide for the Design of Durable Parking Structures
(362.1R-97 (Reapproved 2002)),” ACI Committee 362,
American Concrete Institute, Farmington Hills, MI, 1997, 33 pp.
(This summarizes practical information regarding design of
parking structures for durability. It also includes information
about design issues related to parking structure construction
and maintenance.)
“CRSI Handbook,” Concrete Reinforcing Steel Institute,
Schaumburg, IL, tenth edition, 2008, 777 pp. (This provides

tabulated designs for structural elements and slab systems.
Design examples are provided to show the basis and use of
the load tables. Tabulated designs are given for beams;
square, round, and rectangular columns; one-way slabs; and

one-way joist construction. The design tables for two-way
slab systems include flat plates, flat slabs, and waffle slabs.
The chapters on foundations provide design tables for square
footings, pile caps, drilled piers (caissons), and cantilevered
retaining walls. Other design aids are presented for crack
control and development of reinforcement and lap splices.)
“Reinforcement Anchorages and Splices,” Concrete
Reinforcing Steel Institute, Schaumburg, IL, fifth edition,
2008, 100 pp. (This provides accepted practices in splicing
reinforcement. The use of lap splices, mechanical splices,
and welded splices are described. Design data are presented
for development and lap splicing of reinforcement.)
“Structural Welded Wire Reinforcement Manual of
Standard Practice,” Wire Reinforcement Institute, Hartford,
CT, eighth edition, Apr. 2006, 38 pp. (This describes welded
wire reinforcement material, gives nomenclature and wire
size and weight tables. Lists specifications and properties
and manufacturing limitations. Book has latest code requirements as code affects welded wire. Also gives development
length and splice length tables. Manual contains customary
units and soft metric units.)
“Structural Welded Wire Reinforcement Detailing
Manual,” Wire Reinforcement Institute, Hartford, CT,
1994, 252 pp. (The manual, in addition to including ACI 318
provisions and design aids, also includes: detailing guidance
on welded wire reinforcement in one-way and two-way

slabs; precast/prestressed concrete components; columns
and beams; cast-in-place walls; and slabs-on-ground. In
addition, there are tables to compare areas and spacings of
high-strength welded wire with conventional reinforcing.)
“PCI Design Handbook—Precast and Prestressed
Concrete,” Precast/Prestressed Concrete Institute, Chicago, IL,
seventh edition, 2010, 804 pp. (This provides load tables for
common industry products, and procedures for design and
analysis of precast and prestressed elements and structures
composed of these elements. Provides design aids and examples.)
“Design and Typical Details of Connections for Precast and
Prestressed Concrete,” Precast/Prestressed Concrete Institute,
Chicago, IL, second edition, 1988, 270 pp. (This updates
available information on design of connections for both
structural and architectural products, and presents a full
spectrum of typical details. This provides design aids and
examples.)
“Post-Tensioning Manual,” Post-Tensioning Institute,
Farmington Hills, MI, sixth edition, 2006, 354 pp. (This
provides comprehensive coverage of post-tensioning systems,
specifications, design aids, and construction concepts.)

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CHAPTER 1 — GENERAL REQUIREMENTS

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1.1 — Scope

R1.1 — Scope

1.1.1 — This Code provides minimum requirements
for design and construction of structural concrete
members of any structure erected under requirements
of the legally adopted general building code of which
this Code forms a part. In areas without a legally
adopted building code, this Code defines minimum
acceptable standards for materials, design, and
construction practice. This Code also covers the
strength evaluation of existing concrete structures.

The American Concrete Institute “Building Code Requirements for Structural Concrete (ACI 318M-11),” referred
to as the Code or 2011 Code, provides minimum requirements
for structural concrete design or construction.

For structural concrete, fc′ shall not be less than 17 MPa.
No maximum value of fc′ shall apply unless restricted
by a specific Code provision.

The 2011 Code revised the previous standard “Building
Code Requirements for Structural Concrete (ACI

318M-08).” This standard includes in one document the
rules for all concrete used for structural purposes including
both plain and reinforced concrete. The term “structural
concrete” is used to refer to all plain or reinforced concrete
used for structural purposes. This covers the spectrum of
structural applications of concrete from nonreinforced
concrete to concrete containing nonprestressed reinforcement, prestressing steel, or composite steel shapes, pipe, or
tubing. Requirements for structural plain concrete are in
Chapter 22.
Prestressed concrete is included under the definition of
reinforced concrete. Provisions of the Code apply to
prestressed concrete except for those that are stated to apply
specifically to nonprestressed concrete.
Chapter 21 of the Code contains provisions for design and
detailing of earthquake-resistant structures. See 1.1.9.
Appendix A of Codes prior to 2002 contained provisions for
an alternate method of design for nonprestressed reinforced
concrete members using service loads (without load factors)
and permissible service load stresses. The Alternate Design
Method was intended to give results that were slightly more
conservative than designs by the Strength Design Method of
the Code. The Alternate Design Method of the 1999 Code
may be used in place of applicable sections of this Code.
Appendix A of the Code contains provisions for the design
of regions near geometrical discontinuities, or abrupt
changes in loadings.
Appendix B of this Code contains provisions for reinforcement limits based on 0.75ρb , determination of the strength
reduction factor φ, and moment redistribution that have been
in the Code for many years, including the 1999 Code. The
provisions are applicable to reinforced and prestressed

concrete members. Designs made using the provisions of
Appendix B are equally acceptable as those based on the
body of the Code, provided the provisions of Appendix B
are used in their entirety.

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Appendix C of the Code allows the use of the factored load
combinations given in Chapter 9 of the 1999 Code.
Appendix D contains provisions for anchoring to concrete.

1.1.2 — This Code supplements the general building
code and shall govern in all matters pertaining to
design and construction of structural concrete, except
wherever this Code is in conflict with requirements in
the legally adopted general building code.

R1.1.2 — The American Concrete Institute recommends
that the Code be adopted in its entirety; however, it is recognized that when the Code is made a part of a legally adopted
general building code, the general building code may

modify provisions of this Code.

1.1.3 — This Code shall govern in all matters pertaining
to design, construction, and material properties wherever
this Code is in conflict with requirements contained in
other standards referenced in this Code.
1.1.4 — For cast-in-place footings, foundation walls,
and slabs-on-ground for one- and two-family dwellings
and multiple single-family dwellings (townhouses) and
their accessory structures, design and construction in
accordance with ACI 332M-10 shall be permitted.

R1.1.4 — “Residential Code Requirements for Structural
Concrete” reported by ACI Committee 332.1.1 (This
addresses only the design and construction of cast-in-place
footings, foundation walls supported on continuous footings,
and slabs-on-ground for one- and two-family dwellings and
multiple single-family dwellings [townhouses], and their
accessory structures.)

1.1.5 — For unusual structures, such as arches, bins
and silos, blast-resistant structures, and chimneys,
provisions of this Code shall govern where applicable.
See also 22.1.3.

R1.1.5 — Some structures involve unique design and
construction problems that are not covered by the Code.
However, many Code provisions, such as the concrete
quality and design principles, are applicable for these
structures. Detailed recommendations for design and

construction of some special structures are given in the
following ACI publications:
“Code Requirements for Reinforced Concrete Chimneys
and Commentary” reported by ACI Committee 307.1.2
(This gives material, construction, and design requirements
for circular cast-in-place reinforced chimneys. It sets forth
minimum loadings for the design of reinforced concrete
chimneys and contains methods for determining the stresses
in the concrete and reinforcement required as a result of
these loadings.)
“Standard Practice for Design and Construction of
Concrete Silos and Stacking Tubes for Storing Granular
Materials and Commentary” reported by ACI Committee
313.1.3 (This gives material, design, and construction requirements for reinforced concrete bins, silos, and bunkers and stave
silos for storing granular materials. It includes recommended
design and construction criteria based on experimental and
analytical studies plus worldwide experience in silo design
and construction.)
“Code Requirements for Nuclear Safety-Related Concrete
Structures and Commentary” reported by ACI Committee
349.1.4 (This provides minimum requirements for design and
construction of concrete structures that form part of a nuclear
power plant and have nuclear safety-related functions. The

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code does not cover concrete reactor vessels and concrete
containment structures, which are covered by ACI 359.)
“Code for Concrete Containments” reported by Joint
ACI-ASME Committee 359.1.5 (This provides requirements
for the design, construction, and use of concrete reactor
vessels and concrete containment structures for nuclear
power plants.)

1.1.6 — This Code does not govern design and
installation of portions of concrete piles, drilled piers,
and caissons embedded in ground except for structures
assigned to Seismic Design Categories D, E, and F.
See 21.12.4 for requirements for concrete piles, drilled
piers, and caissons in structures assigned to Seismic
Design Categories D, E, and F.

R1.1.6 — The design and installation of piling fully
embedded in the ground is regulated by the general building
code. For portions of piling in air or water, or in soil not
capable of providing adequate lateral restraint throughout
the piling length to prevent buckling, the design provisions
of this code govern where applicable.
Recommendations for concrete piles are given in detail in
“Design, Manufacture, and Installation of Concrete
Piles” reported by ACI Committee 543.1.6 (This provides
recommendations for the design and use of most types of

concrete piles for many kinds of construction.)
Recommendations for drilled piers are given in detail in
“Design and Construction of Drilled Piers” reported by
ACI Committee 336.1.7 (This provides recommendations
for design and construction of foundation piers 750 mm in
diameter or larger made by excavating a hole in the soil and
then filling it with concrete.)
Detailed recommendations for precast prestressed concrete
piles are given in “Recommended Practice for Design,
Manufacture, and Installation of Prestressed Concrete
Piling” prepared by the PCI Committee on Prestressed
Concrete Piling.1.8

1.1.7 — This Code does not govern design and
construction of slabs-on-ground, unless the slab
transmits vertical loads or lateral forces from other
portions of the structure to the soil.

R1.1.7 — Detailed recommendations for design and
construction of slabs-on-ground and floors that do not
transmit vertical loads or lateral forces from other portions
of the structure to the soil, and residential post-tensioned
slabs-on-ground, are given in the following publications:
“Guide to Design of Slabs-on-Ground” reported by ACI
Committee 360.1.9 (This presents information on the design of
slabs-on-ground, primarily industrial floors and the slabs adjacent to them. The report addresses the planning, design, and
detailing of the slabs. Background information on the design
theories is followed by discussion of the soil support system,
loadings, and types of slabs. Design methods are given for
structural plain concrete, reinforced concrete, shrinkagecompensating concrete, and post-tensioned concrete slabs.)

“Design of Post-Tensioned Slabs-on-Ground,” PTI.1.10
(This provides recommendations for post-tensioned slab-onground foundations. Presents guidelines for soil investigation,
and design and construction of post-tensioned residential and
light commercial slabs on expansive or compressible soils.)

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1.1.8 — Concrete on steel deck

COMMENTARY
R1.1.8 — Concrete on steel deck
In steel framed structures, it is common practice to cast
concrete floor slabs on stay-in-place steel deck. In all cases,
the deck serves as the form and may, in some cases, serve an
additional structural function.

1.1.8.1 — Design and construction of structural
concrete slabs cast on stay-in-place, noncomposite
steel deck are governed by this Code.

R1.1.8.1 — In its most basic application, the noncomposite
steel deck serves as a form, and the concrete slab is designed
to carry all loads, while in other applications the concrete
slab may be designed to carry only the superimposed loads.
The design of the steel deck for this application is described
in “Standard for Non-Composite Steel Floor Deck”
(ANSI/SDI NC-2010).1.11 This Standard refers to ACI 318
for the design and construction of the structural concrete slab.

1.1.8.2 — This Code does not govern the composite
design of structural concrete slabs cast on stay-inplace, composite steel deck. Concrete used in the
construction of such slabs shall be governed by
Chapters 1 through 6 of this Code, where applicable.
Portions of such slabs designed as reinforced concrete
are governed by this Code.

R1.1.8.2 — Another type of steel deck commonly used
develops composite action between the concrete and steel
deck. In this type of construction, the steel deck serves as
the positive moment reinforcement. The design and
construction of composite slabs on steel deck is described in
“Standard for Composite Steel Floor Deck” (ANSI/SDI
C1.0-2006).1.12 The standard refers to the appropriate
portions of ACI 318 for the design and construction of the
concrete portion of the composite assembly. Reference 1.13
also provides guidance for design of composite slabs on steel
deck. The design of negative moment reinforcement to create
continuity at supports is a common example where a portion
of the slab is designed in conformance with this Code.

1.1.9 —Provisions for earthquake resistance

R1.1.9 — Provisions for earthquake resistance

1.1.9.1 — The seismic design category of a structure
shall be determined in accordance with the legally
adopted general building code of which this Code forms
a part, or determined by other authority having jurisdiction
in areas without a legally adopted building code.

R1.1.9.1 — Design requirements for an earthquake-resistant structure in this Code are determined by the Seismic
Design Category (SDC) to which the structure is assigned.
In general, the SDC relates to seismic hazard level, soil
type, occupancy, and use of the building. Assignment of a
building to a SDC is under the jurisdiction of a general
building code rather than ACI 318.
Seismic Design Categories in this Code are adopted directly
from the 2010 ASCE/SEI 7 standard.1.14 Similar designations
are used by the 2009 edition of the “International Building
Code” (IBC),1.15 and the 2009 NFPA 5000 “Building
Construction and Safety Code.”1.16 The “BOCA National
Building Code” (NBC)1.17 and “Standard Building Code”
(SBC)1.18 use Seismic Performance Categories. The 1997
“Uniform Building Code” (UBC)1.19 relates seismic design
requirements to seismic zones, whereas previous editions of
ACI 318 related seismic design requirements to seismic risk
levels. Table R1.1.9.1 correlates Seismic Design Categories
to the low, moderate/intermediate, and high seismic risk
terminology used in ACI 318 for several editions before the
2008 edition, and to the various methods of assigning

design requirements in use in the U.S. under the various

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1

TABLE R1.1.9.1 — CORRELATION BETWEEN
SEISMIC-RELATED TERMINOLOGY IN MODEL
CODES
Code, standard, or resource
document and edition

Level of seismic risk or assigned
seismic performance or design
categories as defined in the Code

ACI 318-08; IBC 2000, 2003, 2006,
2009; NFPA 5000, 2003, 2006, 2009;
ASCE 7-98, 7-02, 7-05, 7-10;
NEHRP 1997, 2000, 2003, 2009

SDC*
A, B

ACI 318-05 and previous editions

Low
seismic
risk

BOCA National Building Code 1993,
1996, 1999; Standard Building Code SPC† A, B
1994, 1997, 1999; ASCE 7-93; 7-95;
NEHRP 1991, 1994
Uniform Building Code
1991, 1994, 1997

Seismic
Zone 0, 1

SDC C

SDC
D, E, F

Moderate/
High
intermediate seismic
seismic risk
risk
SPC C

SPC D, E

Seismic
Zone 2

Seismic
Zone 3, 4

*
SDC = Seismic design category as defined in code, standard, or resource document.
†SPC = Seismic performance category as defined in code, standard, or resource document.

model building codes, the ASCE/SEI 7 standard, and the
NEHRP Recommended Provisions.1.20
In the absence of a general building code that prescribes
earthquake loads and seismic zoning, it is the intent of
Committee 318 that application of provisions for seismic
design be consistent with national standards or model
building codes such as References 1.14, 1.15, and 1.16. The
model building codes also specify overstrength factors, Ωo ,
that are related to the seismic-force-resisting system used
for the structure and used for the design of certain elements.
1.1.9.2 — All structures shall satisfy the applicable
provisions of Chapter 21 except those assigned to
Seismic Design Category A and those otherwise
exempted by the legally adopted general building
code. See 21.1.1.

R1.1.9.2 — Structures assigned to Seismic Design Category

(SDC) A have the lowest seismic hazard and performance
requirements. Provisions of Chapters 1 through 19 and
Chapter 22 are considered sufficient for these structures. For
structures assigned to other SDCs, the design requirements
of Chapter 21 apply, as delineated in 21.1.

1.1.10 — This Code does not govern design and
construction of tanks and reservoirs.

R1.1.10 — Detailed recommendations for design and
construction of tanks and reservoirs are given in “Code
Requirements for Environmental Engineering Concrete
Structures” reported by ACI Committee 350.1.21 (This
gives material, design and construction recommendations
for concrete tanks, reservoirs, and other structures commonly
used in water and waste treatment works where dense,
impermeable concrete with high resistance to chemical
attack is required. Special emphasis is placed on a structural
design that minimizes the possibility of cracking and
accommodates vibrating equipment and other special loads.
Proportioning of concrete, placement, curing, and protection
against chemicals are also described. Design and spacing of
joints receive special attention.)
Guidance for the design and construction of cooling towers and
circular prestressed concrete tanks may be found in the reports
of ACI Committees 334,1.22 350,1.21 372,1.23 and 373.1.24

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1.2 — Contract documents

R1.2 — Contract documents

1.2.1 — Contract documents for all structural concrete
construction shall bear the seal of a licensed design
professional. These contract documents shall show:

R1.2.1 — The provisions for preparation of contract documents
are, in general, consistent with those of most general building
codes and are intended as supplements.

(a) Name and date of issue of code and supplement
to which design conforms;

The Code lists some of the more important items of information that should be included in the contract documents. The
Code does not imply an all-inclusive list, and additional items
may be required by the building official.

(b) Live load and other loads used in design;

(c) Specified compressive strength of concrete at
stated ages or stages of construction for which each
part of structure is designed;
(d) Specified strength or grade of reinforcement;
(e) Size and location of all structural elements and
reinforcement;
(f) Requirements for type, size, location, and installation
of anchors; and qualifications for post-installed
anchor installers as required by D.9;
(g) Provision for dimensional changes resulting from
creep, shrinkage, and temperature;
(h) Magnitude and location of prestressing forces;
(i) Anchorage length of reinforcement and location
and length of lap splices;
(j) Type and location of mechanical and welded
splices of reinforcement;
(k) Details and location of all contraction or isolation
joints specified for structural plain concrete in
Chapter 22;
(l) Minimum concrete compressive strength at time
of post-tensioning;
(m) Stressing sequence for post-tensioning tendons;
(n) Statement if slab-on-ground is designed as a
structural diaphragm, see 21.12.3.4.
1.2.2 — Calculations pertinent to design shall be filed
with the contract documents when required by the
building official. Analyses and designs using computer
programs shall be permitted provided design
assumptions, user input, and computer-generated
output are submitted. Model analysis shall be

permitted to supplement calculations.

R1.2.2 — Documented computer output is acceptable
instead of manual calculations. The extent of input and
output information required will vary according to the
specific requirements of individual building officials.
However, when a computer program has been used, only
skeleton data should normally be required. This should
consist of sufficient input and output data and other information to allow the building official to perform a detailed
review and make comparisons using another program or
manual calculations. Input data should be identified as to
member designation, applied loads, and span lengths. The
related output data should include member designation and

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the shears, moments, and reactions at key points in the span.
For column design, it is desirable to include moment magnification factors in the output where applicable.
The Code permits model analysis to be used to supplement
structural analysis and design calculations. Documentation
of the model analysis should be provided with the related
calculations. Model analysis should be performed by an

individual having experience in this technique.

1.3 — Inspection

R1.3 — Inspection
The quality of concrete structures depends largely on workmanship in construction. The best of materials and design
practices will not be effective unless the construction is
performed well. Inspection is necessary to confirm that the
construction is in accordance with the contract documents.
Proper performance of the structure depends on construction
that accurately represents the design and meets code
requirements within the tolerances allowed. Qualification of
the inspectors can be obtained from a certification
program, such as the ACI Certification Program for Concrete
Construction Special Inspector.

1.3.1 — Concrete construction shall be inspected as
required by the legally adopted general building code. In
the absence of such inspection requirements, concrete
construction shall be inspected throughout the various
Work stages by or under the supervision of a licensed
design professional or by a qualified inspector.

R1.3.1 — Inspection of construction by or under the
supervision of the licensed design professional responsible
for the design should be considered because the person in
charge of the design is usually the best qualified to determine if
construction is in conformance with construction documents.
When such an arrangement is not feasible, inspection of
construction through other licensed design professionals or

through separate inspection organizations with demonstrated
capability for performing the inspection may be used.
Qualified inspectors should establish their qualification by
becoming certified to inspect and record the results of concrete
construction, including preplacement, placement, and postplacement operations through the ACI Inspector Certification
Program: Concrete Construction Special Inspector.
When inspection is done independently of the licensed
design professional responsible for the design, it is recommended that the licensed design professional responsible for
the design be employed at least to oversee inspection and
observe the Work to see that the design requirements are
properly executed.
In some jurisdictions, legislation has established registration
or licensing procedures for persons performing certain
inspection functions. A check should be made in the general
building code or with the building official to ascertain if any
such requirements exist within a specific jurisdiction.
Inspection reports should be promptly distributed to the
owner, licensed design professional responsible for the

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design, contractor, appropriate subcontractors, appropriate
suppliers, and the building official to allow timely identification of compliance or the need for corrective action.
Inspection responsibility and the degree of inspection
required should be set forth in the contracts between the
owner, architect, engineer, contractor, and inspector.
Adequate fees should be provided consistent with the work
and equipment necessary to properly perform the inspection.

1.3.2 — The inspector shall require compliance with
contract documents. Unless specified otherwise in the
legally adopted general building code, inspection
records shall include:
(a) Delivery, placement, and testing reports documenting the quantity, location of placement, fresh
concrete tests, strength, and other test of all classes
of concrete mixtures;
(b) Construction and removal of forms and reshoring;
(c) Placing of reinforcement and anchors;
(d) Mixing, placing, and curing of concrete;
(e) Sequence of erection and connection of precast
members;
(f) Tensioning of tendons;
(g) Any significant construction loadings
completed floors, members, or walls;
(h) General progress of Work.

on

R1.3.2 — By inspection, the Code does not mean that the
inspector should supervise the construction. Rather, it means
that the one employed for inspection should visit the project
with the frequency necessary to observe the various stages
of Work and ascertain that it is being done in compliance
with contract documents and Code requirements. The
frequency should be at least enough to provide general
knowledge of each operation, whether this is several times a
day or once in several days.
Inspection in no way relieves the contractor from the obligation
to follow the contract documents and to provide the designated
quality and quantity of materials and workmanship for all
job stages. Some of the information regarding designated
concrete mixtures on a project is often provided in a
preconstruction submittal to the licensed design professional.
For instance, concrete mixture ingredients and composition
are often described in detail in the submittal and are
subsequently identified by a mixture designation (reflected
on a delivery ticket) that can also identify the placement
location in the structure. The inspector should be present as
frequently as necessary to judge whether the quality, as
measured by quality assurance tests, quantity, and placement
of the concrete comply with the contract documents; to
counsel on possible ways of obtaining the desired results; to
see that the general system proposed for formwork appears
proper (though it remains the contractor’s responsibility to
design and build adequate forms and to leave them in place
until it is safe to remove them); to see that reinforcement is
properly installed; to see that concrete is delivered as
required and is of the correct quality, properly placed, and

cured; and to see that tests for quality assurance are being
made as specified.
The Code prescribes minimum requirements for inspection
of all structures within its scope. It is not a construction
specification and any user of the Code may require higher
standards of inspection than cited in the legal code if
additional requirements are necessary.
Recommended procedures for organization and conduct of
concrete inspection are given in detail in “Guide for
Concrete Inspection” reported by ACI Committee 311.1.25
(This sets forth procedures relating to concrete construction
to serve as a guide to owners, architects, and engineers in
planning an inspection program.)

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STRUCTURAL CONCRETE BUILDING CODE (ACI 318M-11) AND COMMENTARY

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17

COMMENTARY
Detailed methods of inspecting concrete construction are
given in “ACI Manual of Concrete Inspection” (SP-2)
reported by ACI Committee 311.1.26 (This describes
methods of inspecting concrete construction that are generally accepted as good practice. Intended as a supplement to
specifications and as a guide in matters not covered by
specifications.)

1.3.3 — When the ambient temperature falls below
4°C or rises above 35°C, a record shall be kept of
concrete temperatures and of protection given to
concrete during placement and curing.

R1.3.3 — The term “ambient temperature” means the
temperature of the environment to which the concrete is
directly exposed. Concrete temperature as used in this
section may be taken as the surface temperature of the
concrete. Surface temperatures may be determined by
placing temperature sensors in contact with concrete
surfaces or between concrete surfaces and covers used for
curing, such as insulation blankets or plastic sheeting.

1.3.4 — Records of inspection required in 1.3.2 and
1.3.3 shall be preserved by the inspecting engineer or
architect for at least 2 years after completion of the
project.

R1.3.4 — A record of inspection in the form of a job diary is
required in case questions subsequently arise concerning the
performance or safety of the structure or members. Photographs documenting job progress may also be desirable.
Records of inspection should be preserved for at least 2 years
after the completion of the project. The completion of the
project is the date at which the owner accepts the project, or
when a certificate of occupancy is issued, whichever date is
later. The general building code or other legal requirements
may require a longer preservation of such records.

1.3.5 — For special moment frames designed in
accordance with Chapter 21, continuous inspection of
the placement of the reinforcement and concrete shall
be made by a qualified inspector. The inspector shall
be under the supervision of the licensed design
professional responsible for the structural design or
under the supervision of a licensed design professional with demonstrated capability for supervising
inspection of construction of special moment frames.

R1.3.5 — The purpose of this section is to ensure that the
detailing required in special moment frames is properly
executed through inspection by personnel who are qualified
to do this Work. Qualifications of inspectors should be acceptable to the jurisdiction enforcing the general building code.

1.4 — Approval of special systems of
design or construction

R1.4 — Approval of special systems of
design or construction

Sponsors of any system of design or construction within
the scope of this Code, the adequacy of which has been
shown by successful use or by analysis or test, but which
does not conform to or is not covered by this Code, shall
have the right to present the data on which their design is
based to the building official or to a board of examiners
appointed by the building official. This board shall be
composed of competent engineers and shall have
authority to investigate the data so submitted, to require
tests, and to formulate rules governing design and

construction of such systems to meet the intent of this
Code. These rules, when approved by the building
official and promulgated, shall be of the same force
and effect as the provisions of this Code.

New methods of design, new materials, and new uses of
materials should undergo a period of development before
being specifically covered in a code. Hence, good systems
or components might be excluded from use by implication if
means were not available to obtain acceptance.
For special systems considered under this section, specific
tests, load factors, deflection limits, and other pertinent
requirements should be set by the board of examiners, and
should be consistent with the intent of the Code.
The provisions of this section do not apply to model tests
used to supplement calculations under 1.2.2 or to strength
evaluation of existing structures under Chapter 20.

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STRUCTURAL CONCRETE BUILDING CODE (ACI 318M-11) AND COMMENTARY

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Notes

COMMENTARY

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STRUCTURAL CONCRETE BUILDING CODE (ACI 318M-11) AND COMMENTARY

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CHAPTER 2 — NOTATION AND DEFINITIONS
2
2.1 — Code notation

Ah

The terms in this list are used in the Code and as
needed in the Commentary.

Aj

a
av

Ab
Abrg
Ac
Acf

Ach
Acp
Acs
Act
Acv

Acw
Af
Ag

= depth of equivalent rectangular stress block
as defined in 10.2.7.1, mm, Chapter 10
= shear span, equal to distance from center of
concentrated load to either: (a) face of
support for continuous or cantilevered
members, or (b) center of support for simply
supported members, mm, Chapter 11,
Appendix A
= area of an individual bar or wire, mm2,
Chapters 10, 12
= net bearing area of the head of stud, anchor
bolt, or headed deformed bar, mm2, Chapter
12, Appendix D
= area of concrete section resisting shear
transfer, mm2, Chapters 11, 21
= larger gross cross-sectional area of the slabbeam strips of the two orthogonal equivalent
frames intersecting at a column of a two-way
slab, mm2, Chapter 18
= cross-sectional area of a structural member

measured to the outside edges of transverse
reinforcement, mm2, Chapters 10, 21
= area enclosed by outside perimeter of
concrete cross section, mm2, see 11.5.1,
Chapter 11
= cross-sectional area at one end of a strut in
a strut-and-tie model, taken perpendicular to
the axis of the strut, mm2, Appendix A
= area of that part of cross section between
the flexural tension face and center of gravity
of gross section, mm2, Chapter 18
= gross area of concrete section bounded by
web thickness and length of section in the
direction of shear force considered, mm2,
Chapter 21
= area of concrete section of an individual pier,
horizontal wall segment, or coupling beam
resisting shear, mm2, Chapter 21
= area of reinforcement in bracket or corbel
resisting factored moment, mm2, see 11.8,
Chapter 11
= gross area of concrete section, mm2. For a
hollow section, Ag is the area of the concrete
only and does not include the area of the
void(s), see 11.5.1, Chapters 9-11, 14-16,
21, 22, Appendixes B, C

Al
Al,min
ANa

ANao

ANc

ANco

An
Anz
Ao
Aoh
Aps
As
As′
Asc
Ase,N
Ase,V

= total area of shear reinforcement parallel to
primary tension reinforcement in a corbel or
bracket, mm2, see 11.8, Chapter 11
= effective cross-sectional area within a joint in
a plane parallel to plane of reinforcement
generating shear in the joint, mm2, see
21.7.4.1, Chapter 21
= total area of longitudinal reinforcement to
resist torsion, mm2, Chapter 11
= minimum area of longitudinal reinforcement to
resist torsion, mm2, see 11.5.5.3, Chapter 11
= projected influence area of a single adhesive

anchor or group of adhesive anchors, for
calculation of bond strength in tension, mm2,
see D.5.5.1, Appendix D
= projected influence area of a single adhesive
anchor, for calculation of bond strength in
tension if not limited by edge distance or
spacing, mm2, see D.5.5.1, Appendix D
= projected concrete failure area of a single
anchor or group of anchors, for calculation of
strength in tension, mm2, see D.5.2.1,
Appendix D
= projected concrete failure area of a single
anchor, for calculation of strength in tension
if not limited by edge distance or spacing,
mm2, see D.5.2.1, Appendix D
= area of reinforcement in bracket or corbel
resisting tensile force Nuc , mm2, see 11.8,
Chapter 11
= area of a face of a nodal zone or a section
through a nodal zone, mm2, Appendix A
= gross area enclosed by shear flow path,
mm2, Chapter 11
= area enclosed by centerline of the outermost
closed transverse torsional reinforcement,
mm2, Chapter 11
= area of prestressing steel in flexural tension
zone, mm2, Chapter 18, Appendix B
= area of nonprestressed longitudinal tension
reinforcement, mm2, Chapters 10-12, 14, 15,
18, Appendix B

= area of compression reinforcement, mm2,
Appendix A
= area of primary tension reinforcement in a
corbel or bracket, mm2, see 11.8.3.5,
Chapter 11
= effective cross-sectional area of anchor in
tension, mm2, Appendix D
= effective cross-sectional area of anchor in
shear, mm2, Appendix D

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Ash

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STRUCTURAL CONCRETE BUILDING CODE (ACI 318M-11) AND COMMENTARY

= total cross-sectional area of transverse
reinforcement (including crossties) within
spacing s and perpendicular to dimension
bc , mm2, Chapter 21
= total area of surface reinforcement at
Asi
spacing si in the i-th layer crossing a strut,
with reinforcement at an angle αi to the axis
of the strut, mm2, Appendix A

As,min = minimum area of flexural reinforcement,
mm2, see 10.5, Chapter 10
= total area of nonprestressed longitudinal
Ast
reinforcement (bars or steel shapes), mm2,
Chapters 10, 21
Asx = area of structural steel shape, pipe, or tubing
in a composite section, mm2, Chapter 10
= area of one leg of a closed stirrup resisting
At
torsion within spacing s, mm2, Chapter 11
= area of prestressing steel in a tie, mm2,
Atp
Appendix A
= total cross-sectional area of all transverse
Atr
reinforcement within spacing s that crosses
the potential plane of splitting through the
reinforcement being developed, mm2,
Chapter 12
= area of nonprestressed reinforcement in a
Ats
tie, mm2, Appendix A
= area of shear reinforcement within spacing s,
Av
mm2, Chapters 11, 17
Avd = total area of reinforcement in each group of
diagonal bars in a diagonally reinforced
coupling beam, mm2, Chapter 21
= area of shear-friction reinforcement, mm2,

Avf
Chapters 11, 21
Avh = area of shear reinforcement parallel to flexural tension reinforcement within spacing s2,
mm2, Chapter 11
Av,min = minimum area of shear reinforcement within
spacing s, mm2, see 11.4.6.3 and 11.4.6.4,
Chapter 11
AVc = projected concrete failure area of a single
anchor or group of anchors, for calculation
of strength in shear, mm2, see D.6.2.1,
Appendix D
AVco = projected concrete failure area of a single
anchor, for calculation of strength in shear, if
not limited by corner influences, spacing, or
member thickness, mm2, see D.6.2.1,
Appendix D
= loaded area, mm2, Chapters 10, 22
A1
= area of the lower base of the largest frustum
A2
of a pyramid, cone, or tapered wedge
contained wholly within the support and
having for its upper base the loaded area,
and having side slopes of 1 vertical to 2
horizontal, mm2 , Chapters 10, 22
b
= width of compression face of member, mm,
Chapter 10, Appendix B

= cross-sectional dimension of member core

measured to the outside edges of the transverse reinforcement composing area Ash , mm,
Chapter 21
= perimeter of critical section for shear in slabs
bo
and footings, mm, see 11.11.1.2, Chapters
11, 22
= width of strut, mm, Appendix A
bs
= width of that part of cross section containing
bt
the closed stirrups resisting torsion, mm,
Chapter 11
= width of cross section at contact surface
bv
being investigated for horizontal shear, mm,
Chapter 17
= web width, wall thickness, or diameter of
bw
circular section, mm, Chapters 10-12, 21, 22,
Appendix B
= dimension of the critical section bo measured
b1
in the direction of the span for which
moments are determined, mm, Chapter 13
= dimension of the critical section bo measured
b2
in the direction perpendicular to b1, mm,
Chapter 13
= nominal bearing strength, N, Chapter 22
Bn

= factored bearing load, N, Chapter 22
Bu
c
= distance from extreme compression fiber to
neutral axis, mm, Chapters 9, 10, 14, 21
= critical edge distance required to develop the
cac
basic strength as controlled by concrete
breakout or bond of a post-installed anchor
in tension in uncracked concrete without
supplementary reinforcement to control
splitting, mm, see D.8.6, Appendix D
ca,max = maximum distance from center of an anchor
shaft to the edge of concrete, mm, Appendix D
ca,min = minimum distance from center of an anchor
shaft to the edge of concrete, mm, Appendix D
= distance from the center of an anchor shaft
ca1
to the edge of concrete in one direction, mm.
If shear is applied to anchor, ca1 is taken in
the direction of the applied shear. If tension
is applied to the anchor, ca1 is the minimum
edge distance, Appendix D. Where anchors
subject to shear are located in narrow
sections of limited thickness, see D.6.2.4
= distance from center of an anchor shaft to
ca2
the edge of concrete in the direction perpendicular to ca1, mm, Appendix D
= smaller of: (a) the distance from center of a
cb

bar or wire to nearest concrete surface, and
(b) one-half the center-to-center spacing of
bars or wires being developed, mm,
Chapter 12
= clear cover of reinforcement, mm, see
cc
10.6.4, Chapter 10
cNa = projected distance from center of an anchor
shaft on one side of the anchor required to
bc

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STRUCTURAL CONCRETE BUILDING CODE (ACI 318M-11) AND COMMENTARY

ct

=

c1

=

c2

C

=

=

Cm

=

d

=

d′

=

da

=

da′

=

db

=

dp

=

dpile

=

dt

=

D

=

e
eh

=
=

eN′

=

eV′

=

develop the full bond strength of a single
adhesive anchor, mm, see D.5.5.1, Appendix D
distance from the interior face of the column
to the slab edge measured parallel to c1, but

not exceeding c1, mm, Chapter 21
dimension of rectangular or equivalent
rectangular column, capital, or bracket
measured in the direction of the span for
which moments are being determined, mm,
Chapters 11, 13, 21
dimension of rectangular or equivalent
rectangular column, capital, or bracket
measured in the direction perpendicular to
c1, mm, Chapter 13
cross-sectional constant to define torsional
properties of slab and beam, see 13.6.4.2,
Chapter 13
factor relating actual moment diagram to an
equivalent uniform moment diagram,
Chapter 10
distance from extreme compression fiber to
centroid of longitudinal tension reinforcement, mm, Chapters 7, 9-12, 14, 17, 18, 21,
Appendixes B, C
distance from extreme compression fiber to
centroid of longitudinal compression reinforcement, mm, Chapters 9, 18, Appendix C
outside diameter of anchor or shaft diameter
of headed stud, headed bolt, or hooked bolt,
mm, see D.8.4, Appendix D
value substituted for da when an oversized
anchor is used, mm, see D.8.4, Appendix D
nominal diameter of bar, wire, or
prestressing strand, mm, Chapters 7, 12, 21
distance from extreme compression fiber to
centroid of prestressing steel, mm, Chapters 11,18, Appendix B

diameter of pile at footing base, mm,
Chapter 15
distance from extreme compression fiber to
centroid of extreme layer of longitudinal
tension steel, mm, Chapters 9, 10, Appendix C
dead loads, or related internal moments and
forces, Chapters 8, 9, 20, 21, Appendix C
base of Napierian logarithms, Chapter 18
distance from the inner surface of the shaft of a
J- or L-bolt to the outer tip of the J- or L-bolt,
mm, Appendix D
distance between resultant tension load on
a group of anchors loaded in tension and
the centroid of the group of anchors loaded
in tension, mm; eN′ is always positive,
Appendix D
distance between resultant shear load on a
group of anchors loaded in shear in the same
direction, and the centroid of the group of

E

=

Ec

=

Ecb

=

Ecs

=

EI

=

Ep

=

Es

=

fc′

=

f c′

=

fce

=

fci′

=

f ci′

=

fcr′

=

fct

=

fd

=

fdc

=

fpc

=

21

anchors loaded in shear in the same direction,
mm; eV′ is always positive, Appendix D
effects of earthquake, or related internal
moments and forces, Chapters 9, 21,
Appendix C
modulus of elasticity of concrete, MPa, see
8.5.1, Chapters 8-10, 14, 19
modulus of elasticity of beam concrete, MPa,
Chapter 13
modulus of elasticity of slab concrete, MPa,
Chapter 13
flexural stiffness of compression member,
N·mm2, see 10.10.6, Chapter 10
modulus of elasticity of prestressing steel,
MPa, see 8.5.3, Chapter 8
modulus of elasticity of reinforcement and
structural steel, MPa, see 8.5.2, Chapters 8,
10, 14
specified compressive strength of concrete,
MPa, Chapters 4, 5, 8-12, 14, 18, 19, 21, 22,
Appendixes A-D
square root of specified compressive
strength of concrete, MPa, Chapters 8, 9, 11,
12, 18, 19, 21, 22, Appendix D
effective compressive strength of the
concrete in a strut or a nodal zone, MPa,
Chapter 15, Appendix A
specified compressive strength of concrete at
time of initial prestress, MPa, Chapters 7, 18
square root of specified compressive

strength of concrete at time of initial
prestress, MPa, Chapter 18
required average compressive strength of
concrete used as the basis for selection of
concrete proportions, MPa, Chapter 5
average splitting tensile strength of lightweight concrete, MPa, Chapters 5, 9, 11, 12,
22
stress due to unfactored dead load, at
extreme fiber of section where tensile stress
is caused by externally applied loads, MPa,
Chapter 11
decompression stress; stress in the
prestressing steel when stress is zero in the
concrete at the same level as the centroid of
the prestressing steel, MPa, Chapter 18
compressive stress in concrete (after allowance for all prestress losses) at centroid of
cross section resisting externally applied
loads or at junction of web and flange when
the centroid lies within the flange, MPa. (In a
composite member, fpc is the resultant
compressive stress at centroid of composite
section, or at junction of web and flange
when the centroid lies within the flange, due
to both prestress and moments resisted by
precast member acting alone), Chapter 11

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